Control system for vehicle suspension



March 20, 1962 A. E. VOGEL CONTROL SYSTEM FOR VEHICLE SUSPENSION 5Sheets-Sheet 1 Original Filed 001..

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INVENTOR.

BY ARTHUR E. VOG'EL jw whkxz ATTOE E YS' March 20, 1962 A. E. VOGELCONTROL SYSTEM FOR VEHICLE SUSPENSION 3 Sheets-Sheet 2 Original FiledOct.

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INVENTOR.

ARTHUR E. VOGEL BY ATTOR EYS March 20, 1962 A. E. VOGEL 3,026,125

CONTROL SYSTEM FOR VEHICLE SUSPENSION Original Filed Oct. 19, 1955 3Sheets-Sheet 3 INVENTOR. ARTHUR E. 1/065 L JpA-ML QJQZZZZ ATTORNEYS.corrections at the outset of the curve.

United States Patent 1 9 Claims. (Cl. 280124) The present inventionrelates to suspension system for vehicles and more particularly to anovel apparatus for automatically controlling such systems.

This application is a division of my co-pending appli cation Serial No.541,337 filed October 19, 1955 which is a continuation-in-part ofco-pending application Serial No. 519,079 of Arthur E. Vogel filed June30, 1955, now abandoned.

In general, the present apparatus is applied to motor vehicles of thetype which comprise a sprung weight portion supported by four unsprungweight portions each of which includes a wheel and an independent springmeans.

It is one object of the present invention to provide a novel suspensionsystem that incorporates a closed fluid circuit containing acompressible fluid, such as air, that is transferred into and out ofscaled flexible casings, or air springs, connected between the sprungand unsprung weights of the vehicle. According to the present invention,the expenditure of fluid energy required to control the suspensionsystem is decreased through use of a novel fluid circuit for the system,whereby savings in horsepower consumed by the system are realized.

It is another aspect of the present invention to provide a controlsystem which permits completely independent suspension operation at eachof the four unsprung portions of a vehicle, with each of said portionsbeing adapted to sense the particular condition to which it is beingsubjected, and to make an appropriate corresponding variation in theforce exerted by its respective spring means. As a result, improvedcornering characteristics and riding comfort are realized under all roadconditions to which the vehicle is subjected.

It is another aspect of the present invention to provide a controlsystem for vehicle suspensions adapted to maintain a normal suspensionconfiguration between sprung and unsprung weight portions of a vehicle,said control system being adapted to vary the force exerted by thespring means of the vehicle by transferring fluid energy to and fromsuch spring means. Such transfer of fluid energy is instituted after atime delay to prevent response of the control system to road imposedimpacts of a short time duration. After the control system returns thesprung and unsprung weight portions to normal configuration, however,the transfer of fluid is caused to cease without such time delay wherebythe sprung and unsprung weights are positively arrested at normalconfiguration without the occurrence of hunting or oscillation of thesystem above and below the normal configuration datum.

It is another aspect of the present invention to provide a controlsystem for vehicle suspensions which system includes a novel inertiaresponsive switch means that serves to rapidly render inoperative a timedelay mechanism in the control system when the vehicle enters a curve sothat the control system will etiect anti-roll The novel switch meansfurther includes a holding relay for automatically retaining the timedelay mechanism inoperative for a time interval subsequent to completionof the curve so that the control system will rapidly remove thepreviously applied anti-roll correction which was required in the curve.Hence the vehicle will not remain in a banked configuration for a periodafter the vehicle completes the curve and ice the passengers of thevehicle will not be subjected to transition sensations as the vehicleleaves a curve and enters a stretch of straight road.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being bad to the accompanyingdrawings wherein preferred forms of embodiments of the invention areclearly shown.

In the drawing:

FIG. 1 is a side sectional view constructed according to the presentinvention;

FIGURE 2 is a diagrammatic view of a novel control system and fluidcircuit constructed according to the present invention;

FIGURE 3 is a top elevational view of a fluid actuated valve unitcomprising a portion of the control means of FIGURE 1;

FIGURE 4 is a bottom elevational view of the fluid actuated valve unitof FIGURE 3; and

FIGURE 5 is a diagrammatic view showing a novel electric controlapparatus utilized with the control means of the present invention andcomprising still another aspect thereof.

Referring in detail to the drawing, FIGURE 2 illustrates a suspensionsystem constructed according to the present invention. The sprung weightof a vehicle is indicated at 20 and the unsprung weight of said vehicleis indicated at 22. A resilient arm 102 is connected to a rod 104 by apivot pin 106. This rod 104 is suitably attached to the unsprung weight22. The lower end of a rod is fastened to resilient arm 102 by a pin120, and the arm 102 is connected to the valve casing 200 by pivot pin103. The upper end of rod 115 is operatively connected to a controlmeans 200, later to be described in detail.

For the sake of simplicity, a compressor 40, is shown as of thereciprocating type including a cylinder 202, having an air inlet valve203 and an air outlet valve 20%. Valve 203 is upwardly urged towards theclosed position by a spring 206, and valve 204 is downwardly urgedtowards the closed position by a spring 207. The compressor alsoincludes a reciprocating piston 209 which is connected with a crankshaft 210 by a connecting rod 211. The shaft of the compressor is shownat 213. Compressed air is forced through the outlet valve 294 and line214 to a high pressure reservoir 215. Air is fed to the compressorthrough valve 263 from a relatively low pressure reservoir 216 via line217.

A control means 200 is provided for each of the sealed casings 80 andeach is fed from the high pressure reservoir 215 through a line 219,control means 200, and line 220. Air is exhausted from each of thecasings 80 to the pipe 220, control means 200, and line 221, one linebeing provided for each of the four chambers 80.

Instead of exhausting the air from the chamber 80 to atmosphere, thelines 221 are connected to the relatively low pressure reservoir 216.This reservoir is provided with an inlet valve 223 which is urged toclosed position by a spring 224. Such spring is of light constructionand is merely used to hold the valve closed in the event that the airwithin the reservoir 216 is at atmospheric pressure. Normally, however,the pressure within reservoir 216 is substantially above atmosphericpressure. Air cannot escape reservoir 216 except through line 217 or apressure relief valve 226. As an example, the air pressure normallyexisting within the relatively low pressure reservoir 216 is at fortypounds per square inch, that in the chamber 80 is approximately 80pounds per square inch, and that in the high pressure reservoir 215approximately pounds per square inch. Far less energy is expended inraising the pressure from 40 pounds per square inch to 120 pounds persquare inch than would be expended in increasing the pressure ofatmospheric air to 120 pounds per square inch. Thus by maintaining apressure of 40 pounds per square inch, for example, in the relativelylow pressure reservoir 216, the system is operated more economically.The maximum high pressure within reservoir 215 can be controlled by acontroller 228 which includes a chamber 229 connected by a line 230 tothe reservoir 215. One of the walls 231 of the controller 228 isflexible and a rod 234 is engageable with the top of inlet valve 203.When the pressure within the reservoir 215 attains the desired maximum,valve 203 will be forced downwardly by the diaphragm 2'31 and rod 234 topartly open the inlet valve 203. By partially opening valve 203, andpreventing it from returning to its seat, the air is merely oscillatedbetween the line 217 and the cylinder 202. After the requirements ofchambers 80 cause the pressure in high pressure reservoir 215 to dropbelow the maximum at which the controller 228 opens the intake valve203, then the intake valve 203 will be returned to its seat andcompressor 40 will resume normal operation and supply air to the highpressure reservoir 215.

Referring next to FIGURE 1, control means 200 includes a spool 52slideahly fitted in a cylinder 37 and provided with a necked portion 54.When spool 52 moves upwardly, high pressure reservoir 215 delivers airthrough line 219 to flexible casing 80 since line 220 is then connectedto line 219 by necked portion 54 of the spool.

When spool 52 moves downwardly from the position illustrated in FIGURE1, flexible casing 80 is connected to low pressure reservoir 216 sincethe port 41, and hence the line 221, are connected to line 220 by thenecked portion 54 of the spool.

When spool 52 is in the normal position illustrated in FIGURE 1, whichis the case when no correction for static or inertia load variation isbeing made by the control means, then the interior of flexible casing 80is isolated from both reservoirs 215 and 216 and the reservoirs areisolated from each other, since spool 52 is then effect.- ing isolationof the lines 219, 220, and 221, one from the other.

With continued reference to control means 200, spool 52 is connected toresilient arm 102 by a rod 115 which rod extends slideahly through anupper removable Wall 116 and a lower removable wall 117 of a chamber118. The lower end of rod 115 is pivotally and slideahly connectedtoresilient arm 102 by a pin 120 extended through a slot 121.

A valve movement retarding means, indicated generally at 124, is mountedon rod 115 and in sealed sliding engagement with the inner wall ofchamber 118.

Retarding means 124 is illustrated in the normal position it occupieswhen the suspension system is in a normal configuration shown in FIGURE1 in which configuration the sprung weight is a normal static loaddistance from the unsprung weight 22 and the spool 52 is efiectingisolation of lines 219, 220, and 221, one from the other.

When retarding means 124 is urged upwardly or downwardly, from thenormal position illustrated, fluid will be moved, respectively, from anupper chamber portion 126 to a lower chamber portion 127, or from lowerchamber portion 127 to upper chamber portion 126. As long as valveelement 129 of a time delay valve 130 closes passage 131, as illustratedin FIGURE 1, fluid moving between chamber portions 126 and 127 must passthrough a passage 132. This passage 132 is provided with a restrictor133 which may be formed as an adjustable threaded needle valve 133carried by lower casing 111 .and extended into the lower end of passage132. It will be understood that the rate of movement of retarding means124, either upwardly or downwardly from the normal position illustrated,is much slower while the valve element 129 closes the larger passage 131since, in such instance, the flow rate of fluid between chamber portions126 and 127 is, throttled by the restrictor 133. When valve element 129of time delay valve is removed from passage 131, however, the fluid canrapidly move between the chamber portions 126 and 127 and the retardingmeans 124, and spool 52 connected thereto, can move rapidly wherebycorrections are rapidly instituted by control means 200.

When the time delay mechanism is operative, and rapid movement ofretarding means 124 away from the normal position is prevented, then theresilient arm 102 will bend upwardly or downwardly with rapid relativemovement between the sprung and unsprung weight portions, yet when oneof such relative movements is retained for a time duration greater thanthe time delay of the system then such arm provides the necessary forcefor continuing the movement of retarding means 124 at the slow rate itmust move while time delay valve 130 closes passage 131. Hence it isseen that the resilient arm 102 allows rapid relative movement betweensprung and unsprung weight portions 20 and 22 at times when movement ofretarding means 124 is retarded and cannot follow such rapid relativemovements. Accordingly, the control means is rendered inoperative whenroad imposed impacts of short time duration are encountered. When thevehicle encounters a static load change of relative long time duration,however, such as occurs when the number of passengers is increased ordecreased, the resilient arm 102 will bend and continue'to bias theretarding means 124 until slow movement thereof moves spool 52 to theappropriate position for the correction required to return the sprungand unsprung weight portions 20 and 22 to the normal configuration atwhich they are spaced a predetermined distance apart.

When retarding means 124 is urged upwardly by resilient arm 102, as willoccur when sprung weight 20 moves downwardly relative to unsprung weight22, an upper resilient valve member 136 is maintained closed by fluidpressure whereby fluid cannot pass through the passages 137, 138, or 139to lower chamber 127. Hence fluid is moved either through restrictedpassage 132 or through both the restricted passage 132 and the largerpassage 131 depending on whether or not time delay valve 130 is open orclosed.

After retarding means 124 has been moved upwardly, either rapidly orslowly depending on whether or not the time delay valve 130 is open orclosed, such retarding means 124 will always move rapidly back to thenormal position illustrated, after a correction has been made by thecontrol means. Such rapid return of the retarding means 124 occurs whensuch retarding means is returning to the central position illustratedsince the recess 140 is then in communication with lower chamber portion127 whereby fluid pressure in such lower chamber portion 127 and recess140 opens the resilient valve member 136 and fiuid can pass readilythrough passages 137 and 138 and into upper chamber portion 126. Sincethe cross-sectiontal areas of passages 137 and 138 are much greater thanthe effective cross-sectional area of passage 132 at restrictor 133, thefluid transferred between chamber portions 127 and 126 will not slowdown movement of retarding means 124 when such means is returning froman upper position until it reaches the normal position illustrated andcloses by-pass recess 140.

When retarding means 124 is urged downwardly by resilient arm 102, aswould occur when the sprung weight 20 rises relative to unsprung weight22, then the lower resilient valve member 141 will be maintained closedby fluid pressure and fluid will pass from lower chamber portion 127 toupper chamber portion 126 either through the restricted passage 132 orthrough both the restricted passage 132 and the larger passage 131depending on whether the element 129 of time delay valve 130 is in theclosed or open position.

Retarding means 124 will return rapidly from a lower position to thenormal position illustrated since upper chamber portion 126 is then incommunication with recess 14%) whereby fluid ressure opens resilientvalve member 141 and fluid can pass directly through the passages 13Sand 139 and into the lower chamber portion 127 without being forcedthrough the restricted passage 13-2 until retarding means 124 closesby-pass recess 14s).

When retarding means 124 arrives at the normal position illustrated, atthe completion of a return movement after a correction has been made,the side of retarding means 124 forms a closure for recess 14% in themanner illustrated in FIGURE 1.

With continued reference to FIGURE 1, a solenoid 16 and core 161 of thetime delay valve 130 are mounted in a recess in an upper casing portion110. A separate casing portion 184 forms a vertical passage 185 whichconnects reservoir 182 with the chamber portions 126 and 127 by passage164 through core 161 and passage 153.

For controlling the flow of liquid from reservoir 182 to the chamberportions 126 and 127, a fluid actuated valve unit, indicated generallyat 187, is mounted in casing portion 184 below the reservoir 182. Fluidactuated valve unit 187 further provides an escape for any air bubbleswhich may be present in the hydraulic liquid contained in the controlmeans 201 Such unit 137 includes a lower resilient valve member 188which prevents the movement of liquid from chamber portions 126 and 127through passages 189 to reservoir 182 when retarding means 124 isactuated. An upper resilient valve member 199 serves to retain passages191 closed against fluid flow to reservoir 182 up to a predeterminedfluid pressure required in chamber portions 126 and 127 for properoperation of the time delay mechanism located therein. The lowerresilient valve member 183 is mranged to permit free passage ofhydraulic liquid from reservoir 182 through passages 189 to chamberportions 126 and 127 so that such chambers are always maintained full ofliquid notwithstanding any slight leakage which may be present in thehydraulic system.

FIGURE 3 is a top view of fluid actuated valve unit 137 showing upperresilient valve member 196 overlying the passages 191 but being oflesser diameter than the unit whereby the upper ends of passages 189 areuncovered. FIGURE 4 is a bottom view of valve unit 187 showing the lowerresilient member 188 underlying the passages 189 and provided with holescorresponding with the locations of passages 191 whereby the lower endsof such passages are alway open to the entry of fluid.

The control means 200 of the system of FIGURE 2 may be provided with aninertia responsive control means to rapidly render the time delaymechanism inoperative when the vehicle is suddenly subjected to ahorizontally exerted inertia force such as is the case when the vehicleenters a curve, or at the outset of a braking or accelerating operation.In these instances of vehicle operation, it is desirable to rapidlyinstitute an anti-roll correction at the entry of a curve, or to rapidlyresist longitudinal pitching or nose dive of the front of the vehiclewhen the brakes are applied, or to rapidly resist longitudinal pitchingof the vehicle during rapid acceleration thereof. By rapidly institutingthe correction to be made by the control means, through renderinginoperative the time delay mechanism, lower control means pressures arere quired to efiect stability and the passengers of the vehicle will notbe subjected to unpleasant transition sensations as would be the casewere the vehicle permitted to materially proceed into a roll or pitchingmovement before the appropriate correction is instituted by the controlmeans 101 With reference to FIGURE 1, a horizontally disposed mercuryswitch is generally indicated at 165. Such switch includes a tube 166having inclined opposite ends provided with a first pair of contacts 168and a second pair of contacts 170. A source of electric energy 172 isconnected to one of the contacts 168 by wire 173 and the other of thecontacts 158 is connected by wire 174 to a holding relay 171, later tobe described herein, which relay is in turn connected to solenoid by thewire 175. At the other end of tube 166 one of the contacts 170 isconnected to the source of electric energy 172 by the wire 177 and theother of the contacts 170 is connected to the holding relay by the wire178.

When the quantity of mercury 167 connects either the contacts 163 or thecontacts 170 the solenoid 161) is actuated whereby the time delaymechanism is rendered inoperative. It will be understood that when thelongitudinal axis of mercury switch 165 is disposed transversely to thelongitudinal axis of the Vehicle the mercury switch 165 will sensecentrifugal force and render inoperative the time delay mechanism whenthe vehicle encounters a curve.

The same control means 239 can be also utilized to control longitudinalpitching or nose dive of the vehicle when the brakes are applied inslowing down or stopping. In such instances it is desirable to renderinoperative the time delay mechanism of control means 200 so that ananti-pitch correction will be rapidly instituted before the vehicle hasmaterially progressed into a pitched attitude. To accomplish this abrake operated switch 240, illustrated in FIGURE 5 and later to bedescribed, may be connected in parallel with the mercury switch 165.Hence a single control circuit, using both mercury switch 165 and brakeoperated switch 24%), can be utilized with control means 269 wherebysuch control means 100 will eilect both anti-roll corrections andanti-pitch corrections.

Reference is next made to FIGURE 5 which diagrammatically illustrates anelectrical sensing apparatus adapted to operate the time delay mechanismof the previously described control means 200. A mercury switch 165 isprovided with a pair of contact points 168 at one inclined end of ahorizontal tube 166 and a second pair of contacts 176 at the otherinclined end of the horizontal tube 166. When the quantity of mercuryconnects either of the pair of contacts 168 or 171), which occurs whenthe vehicle encounters centrifugal force at curve entry, a solenoid 242of holding relay 171 is energized and a core becomes magnetized wherebypivoted arm 245 pivots on pin 246 and moves downwardly against theaction of tension spring 243 to make contact between an upper contact248 and a lower contact 249.

The mercury switch contacts 168 connect the source of electricity 172with solenoid 242 by Wires 173 and 178. The other mercury switchcontacts connect source 172 with solenoid 242 by wires 173 and 178.

A fluid actuated switch 240 is provided in parallel with mercury switch165 to render inoperative the electrically operated time delay valve 130located within the control means 2% when the vehicle encounters aninertia force which would cause longitudinal pitch of the vehicle. Suchwould occur when the vehicle is to he suddenly decelerated or stopped.Switch 240 includes a fluid chamber 252 fitted with a piston 253. A line254 leading from chamber 252 can be connected to the hydraulic brakesystem of the vehicle, or to another suitable source of pressurizedfluid. When chamber 252 is pressurized, piston 253 moves upwardlyagainst the action of a return spring 256 whereby piston 253electrically connects a pair of contacts 257 and 258. The contacts 257and 258 energize solenoid 242 of holding relay 171 with the source ofelectric energy by the wires 173 and 178.

The upper contact 248 of relay 171 is provided with an adjustable stopprovided by a screw 260 adjustably carried by a dielectric bracket 261mounted on metallic base 262 which base also adjustably supports lowercontact 249. The dielectric bracket 261 insulates upper contact 248 fromlower contact 249 when the former is in the upper position illustrated.The base 262 serves as a conductor between lower contact 249 and a wire175 which leads to the solenoid 160 of time delay valve 130 withincontrol means 200.

When contact 243 engages contact 249 by action of parallel with solenoid242 of the holding relay.

V solenoid 242, then the solenoid 160 of time delay valve 130 isconnected to the source of electric energy by Wires 173, 179, arm 245,contact 248, contact 249, and wire 175. As seen in FIGURE 1, the element129 opens the larger passage 131 whereby retarding means 124, and hencespool 52, will move rapidly to quickly institute an antiroll oranti-pitch correction as required.

With continued reference to FIGURE 5, when the vehicle leaves a curveand enters a stretch of straight road it is desirable to continue to.maintain the time delay mechanism inoperative for a period of time afterthe centrifugal force has ceased and'the mercury switch 165 has brokencontact, in order that the control means 200 can rapidly, without timedelay, make corrections in flexible casing 80, FIGURE 2, whichcorrections are required because centrifugal force is ceasing and theunequal spring forces, requiredin the curve to level the vehicle, are nolonger required in the straight stretch of road being entered. Hence itis desirable to maintain the time delay mechanism inoperative and hencethe solenoid 160 of the time delay switch 130, FIGURE 1, and thesolenoid 242 of the holding relay 171 must both be maintained energized.

To maintain solenoids 242 and 160 energized after mercury switch 165 orthe brake operated fluid actuated switch 240 has broken contact, acondenser 265 is connected in The plates 266 of the condenser areconnected to wire 178 and plates 267 of the condenser are grounded by awire 268.

When one of the switches 165 or 240 connects the source of electricenergy 172 to the solenoid 242 of the holding relay, arm 245 isattracted downwardly to connect contacts 248 and 249 and condenser-.265is charged. So long as switch 162 or 240 is closed, the time delayswitch 130 in control means 200 will remain connected to the source 172and receive electric current therefrom. When the closed switch 165 or240 is opened, as occurs in coming out of a curve or when the brakepressure used in stopping is decreased, then the condenser 265 willbegin to release its stored charge and continue to discharge for a timeinterval whereby solenoid 242 remains energized and the contacts 248 and249 are maintained in engagement subsequent to opening of switch 165 or240.

When condenser 265 discharges the arm 245 is moved upwardly against stop260 whereby time delay valve 130 is closed and control means 200 isrendered non-responsive to road imposed impacts of short time durationin the manner previously described.

It will be understood that each of the control means 200 of the presentinvention can be applied to each of the four wheels of a motor vehiclewhereby anti-roll control, as Well as corrections for variations instatic weight change, is eifected at each of the four wheels of thevehicle. As an alternative, if it is desired to effect antiroll controlat only say the front wheels of the vehicle, then a control means 200would be applied at each of the front wheels of the vehicle, and astructurally more simple and less expensive control means, without atime delay control valve such as solenoid operated time delay controlvalve 130, could be utilized at the rear wheels of the vehicle. In suchlatter instance, corrections for static weight distribution would bemade by a control means at each of the four wheels, but only the controlmeans 200 at the right front wheel and the control means '200 at theleft front wheel would rapidly institute antithat other forms might beadopted, all coming within the scope of the claims which follow:

I claim:

1. In a vehicle of the type having an unsprung weight and a sprungweight, the combination of means interposed between said weightcomprising an expansible and contractible air container; an airreservoir having an outlet connected with the container for supplyingair to the container; a second air reservoir having an inlet connectedwith the container; valve means for controlling the flow of air from thefirst reservoir to the container and for controlling the flow of airfrom the container under pressure above atmospheric pressure to thesecond mentioned reservoir; an air compressor having a low pressure sideand a high pressure side, said low pressure side being connected withthe second mentioned reservoir, and said high pressure side beingconnected with the first mentioned reservoir, said air reservoirs, aircontainer and compressor forming a circuit closed to atmosphere and saidcompressor maintaining a pressure above atmospheric pressure in saidclosed circuit; and pressure responsive valve means for maintaining thepressure in the second mentioned reservoir above atmospheric pressure,said second mentioned valve means including a valve for controlling theflow of air from the second reservoir to the compressor; and meansresponsive to pressure in the first mentioned reservoir for controllingsaid valve.

2. A system as defined in claim 1 characterized to include meansresponsive to a condition to which the vehicle is subjected foractuating the first mentioned valve means to control the flow of airfrom said air container to the second mentioned reservoir.

3. The apparatus defined in claim 1 wherein said first mentioned valvemeans includes a movable flow control element; and means forming aresilient connection between said movable fiow control element and oneof said weights.

4. The apparatus defined in claim 1 wherein said first mentioned valvemeans includes a movable fiow control element; means forming a resilientconnection between said movable flow control element and one of saidweights; and fluid actuated retarding means for controlling the rate ofmovement of said flow control element.

5. The apparatus defined in claim 1 wherein said second mentioned valvemeans includes an air intake valve connected to atmosphere.

6. The apparatus defined in claim 1 wherein said second mentioned valvemeans includes a pressure relief valve.

7. The apparatus defined in claim 1 wherein said second mentioned valvemeans includes a self-closing inlet valve and a pressure relief valve.

8. The apparatus defined in claim 1 wherein said valve forms the intakevalve for said compressor.

9. The apparatus defined in claim 1 wherein said last mentioned meansincludes a movable wall means exposed to pressure in said firstmentioned reservoir and engageable with said valve.

References Cited in the file of this patent UNITED STATES PATENTS1,105,805 Liebowitz Aug. 4, 1914 1,240,664 Brown Sept. 18, 19171,648,908 Mercier Nov. 15, 1927 1,653,110 Valley Dec. 20, 1927 1,664,510Hughes Apr. 3, 1928 2,361,575 'Ilhompson Oct. 31, 1944 2,475,701 EatonJuly 12, 1949 2,778,656 May Ian. 22, 1957

